Zirconium oxide anodic films: Optical and structural properties

The photoluminescence of anodically prepared ZrO(2) films was investigated. Morphological and microstructural analyses reveal an oxide surface covered by a high distribution of blisters and the major crystallographic structure is the monoclinic phase with small quantities of tetragonal phase. The photoluminescence reveals a broad emission band in the range between 350 and 650 nm. It was proposed that the photoluminescence mechanism is originated from the emission of a recombination center related to defects (oxygen vacancies) formed during Zr anodization. (C) 2008 Elsevier B.V. All rights reserved.

Intense violet-blue photoluminescence in BaZrO3 powders: A theoretical and experimental investigation of structural order-disorder

Intense violet-blue photoluminescence (PL) emission at room temperature was verified in BaZrO3 (BZO) powders with structural order-disorder. Ab-initio calculations, ultraviolet-visible absorption spectroscopy and PL were performed. Theoretical results showed that the local disorder in the network-formed Zr clusters present an important role in the formation of hole-electron pair. The experimental data and theoretical results are in agreement, indicating that the PL emission in BZO powders can be related to the structural order-disorder degree in the lattice. (C) 2008 Elsevier B.V. All rights reserved.

Internal Residual Stress Measurements in a Bioactive Glass-Ceramic Using Vickers Indentation

The residual stress distribution that arises in the glass matrix during cooling of a partially crystallized 17.2Na(2)O-32.1CaO-48.1SiO(2)-2.5P(2)O(5) (mol%) bioactive glass-ceramic was measured using the Vickers indentation method proposed by Zeng and Rowcliffe (ZR). The magnitude of the determined residual stress at the crystal/glass boundary was 1/4-1/3 of the values measured using X-ray diffraction (within the crystals) and calculated using Selsing`s model. A correction for the crack geometry factor, assuming a semi-elliptical shape, is proposed and then good agreement between experimental and theoretical values is found. Thus, if the actual crack geometry is taken into account, the indentation technique of ZR can be successfully used. In addition, a numerical model for the calculation of residual stresses that takes into account the hemispherical shape of the crystalline precipitates at a free surface was developed. The result is that near the sample surface, the radial component of the residual stress is increased by 70% in comparison with the residual stress calculated by Selsing`s model.

Mafic dykes at the southwestern margin of Eastern Ghats belt: Evidence of rifting and collision

The southwestern margin of the Eastern Ghats Belt characteristically exposes mafic dykes intruding massif-type charnockites. Dykes of olivine basalt of alkaline composition have characteristic trace element signatures comparable with Ocean Island Basalt (OIB). Most importantly strong positive Nb anomaly and low values of Zr/Nb ratio are consistent with OIB source of the mafic dykes. K-Ar isotopic data indicate two cooling ages at 740 and 530 Ma. The Pan-African thermal event could be related to reactivation of major shear zones and represented by leuco-granite vein along minor shear bands. And 740 Ma cooling age may indicate the low grade metamorphic imprints, noted in some of the dykes. Although no intrusion age could be determined from the present dataset, it could be constrained by some age data of the host charnockite gneiss and Alkaline rocks of the adjacent Prakasam Province. Assuming an intrusion age of similar to 1.3 Ga, Sr-Nd isotopic composition of the dykes indicate that they preserved time-integrated LREE enrichment. In view of the chemical signatures of OIB source, the mafic dykes could as well be related to continental rifting, around 1.3 Ga, which may have been initiated by intra-plate volcanism.

Major- and trace-element composition of REE-rich turkestanite from peralkaline granites of the Morro Redondo Complex, Graciosa Province, south Brazil

Turkestanite, a rare Th- and REE-bearing cyclosilicate in the ekanite-steacyite group was found in evolved peralkaline granites from the Morro Redondo Complex, south Brazil. It occurs with quartz, alkali feldspar and an unnamed Y-bearing silicate. Electron microprobe analysis indicates relatively homogeneous compositions with maximum ThO(2), Na(2)O and K(2)O contents of 22.4%, 2.93% and 3.15 wt.%, respectively, and significant REE(2)O(3) abundances (5.21 to 11.04 wt.%). The REE patterns show enrichment of LREE over HREE, a strong negative Eu anomaly and positive Ce anomaly, the latter in the most transformed crystals. Laser ablation inductively coupled plasma mass spectrometry trace element patterns display considerable depletions in Nb, Zr, Hf, Ti and Li relative to whole-rock sample compositions. Observed compositional variations suggest the influence of coupled substitution mechanisms involving steacyite, a Na-dominant analogue of turkestanite, iraqite, a REE-bearing end-member in the ekanite-steacyite group, ekanite and some theoretical end-members. Turkestanite crystals were interpreted as having precipitated during post-magmatic stages in the presence of residual HFSE-rich fluids carrying Ca, the circulation of which was enhanced by deformational events.

ASSOCIATED A-TYPE SUBALKALINE AND HIGH-K CALC-ALKALINE GRANITES IN THE ITU GRANITE PROVINCE, SOUTHEASTERN BRAZIL: PETROLOGICAL AND TECTONIC SIGNIFICANCE

The 590-580 Ma Itu Granite Province (IGP) is a roughly linear belt of post-orogenic granite plutons similar to 60 km wide extending for some 350 km along the southern edge of the Apia-Guaxupe Terrane in southeastern Brazil. Typical components are subalkaline A-type granites (some with rapakivi texture) that crystallized at varied, but mostly strongly oxidizing conditions, and contrast with a coeval association of also oxidized high-K calc-alkaline granites in terms of major (e. g., lower Ca/Fe) and trace elements (higher Nb, Y, Zr). Mantle-derived magmas (such as those forming the LILE-rich Piracaia Monzodiorite, with epsilon(Nd(t)) = -7 to -10, (87)Sr/(86)Sr((t)) = 0.7045-0.7055) are inferred to derive from enriched subcontinental lithosphere modified during previous subduction, and may have played a role in the generation of the A-type granites, adding melts or fluids or both to the lower crust from which the latter were generated. The IGP is interpreted as a reflection of crust uplift and increased heat flux during ascent of hot, less dense asthenosphere after continental collision, probably reflecting breakoff of an oceanic slab coeval to the right-lateral accretion of a terrane related to the Mantiqueira Orogenic System.

A geochemical and lead isotopic record from a small pond in a remote equatorial island, Fernando de Noronha, Brazil

A 72 cm long core was collected from Lagoa da Viracao (LV), a small poind in the Fernando de Noronha island, northern Brazil. Sediments from the lower section of the core (20-72 cm depth) contain essentially mineral matter, while in the upper section (0-20 cm depth) mineral matter is mixed with organic matter. Lithogenic conservative elements - Si, Al, Fe, Ti, Co, Cr, Cu, Ba, Ga, Hf, Nb, Ni, Y, V, Zn, Zr and REE - exhibit remarkably constant values throughout the core, with concentrations similar to those of the bedrock. The vertical distribution of soluble elements - Ca, Mg, Na, K, P, Mn and Sr - is also homogeneous, but these elements are systematically depleted in relation to the bedrock. LOI, TOC, Br, Se, Hg and Pb, although showing nearly constant values in the lower section of the core, are significantly enriched in the upper section. The concentration profiles of Br and Se suggest that they may be accounted for by natural processes, related to the slight affinity of these elements for organic matter. On the other hand, the elevated levels of Hg and Pb in recent sediments may be explained by their long-range atmospheric transport and deposition. Furthermore, the isotopic composition of Pb clearly indicates that anthropogenic sources contributed to the Pb burden in the uppermost pond sediments.

The direct determination of rare earth elements in basaltic and related rocks using ICP-MS: Testing the efficiency of microwave oven sample decomposition procedures

Tests are described showing the results obtained for the determination of REE and the trace elements Rb, Y, Zr, Nb, Cs, Ba, Hf, Ta, Pb, Th and U with ICP-MS methodology for nine basaltic reference materials, and thirteen basalts and amphibolites from the mafic-ultramafic Niquelandia Complex, central Brazil. Sample decomposition for the reference materials was performed by microwave oven digestion (HF and HNO(3), 100 mg of sample), and that for the Niquelandia samples also by Parr bomb treatment (5 days at 200 degrees C, 40 mg of sample). Results for the reference materials were similar to published values, thus showing that the microwave technique can be used with confidence for basaltic rocks. No fluoride precipitates were observed in the microwave-digested solutions. Total recovery of elements, including Zr and Hf, was obtained for the Niquelandia samples, with the exception of an amphibolite. For this latter sample, the Parr method achieved a total digestion, but not so the microwave decomposition; losses, however, were observed only for Zr and Hf, indicating difficulty in dissolving Zr-bearing minerals by microwave acid attack.

Lacustrine sediments provide geochemical evidence of environmental change during the last millennium in southeastern Brazil

A 172 cm-long sediment core was collected from a small pristine lake situated within a centripetal drainage basin in a tropical karst environment (Ribeira River valley, southeastern Brazil) in order to investigate the paleoenvironmental record provided by the lacustrine geochemistry. Sediments derived from erosion of the surrounding cambisoils contain quartz, kaolinite, mica, chlorite and goethite. Accelerator mass spectroscopy (AMS) (14)C dating provided the geochronological framework. Three major sedimentary units were identified based on the structure and color of the sediments: Unit III from 170 to 140 cm (1030 +/- 60-730 +/- 60 yr BP), Unit II from 140 to 90 cm (730 +/- 60-360 +/- 60 yr BP) and Unit I from 90 to 0 cm (360 +/- 60-0 yr BP). Results of major and trace element concentrations were analysed through multivariate statistical techniques. Factor analysis provided three factors accounting for 72.4% of the total variance. F1 and F2 have high positive loadings from K, Ba, Cs, Rb, Sr, Sc, Th, light rare earth element (LREE), Fe, Cr, Ti, Zr, Hf and Ta, and high negative loadings from Mg, Co, Cu, Zn, Br and loss on ignition (LOI). F3, with positive loadings from V and non-metals As and Sb, accounts for a low percentage (9.7%) of the total variance, being therefore of little interpretative use. The profile distribution of F1 scores reveals negative values in Units I and III, and positive values in Unit II, meaning that K, Ba, Cs, Rb, Sr, Sc, Th, LREE, Fe, Cr, Ti, Zr, Hf and Ta are relatively more concentrated in Unit II, and Mg, Co, Cu, Zn and Br are relatively more abundant in Units I and III. The observed fluctuations in the geochemical composition of the sediments are consistent with slight variations of the erosion intensity in the catchment area as a possible response to variations of climatic conditions during the last millennium. (c) 2009 Elsevier GmbH. All rights reserved.

Chemical and radiological characterization of clay minerals used in pharmaceutics and cosmetics

Since the early days, clays have been used for therapeutic purposes. Nowadays, they are used as active ingredients or as excipient in formulations for a variety of purposes. Despite their wide use, little information is available in literature on their content of trace elements and radionuclides. The purpose of this study was to determine the elements (As, Ba, Br, Cs, Co, Cr, Eu, Fe, Hf, Hg, La, Lu, Rb, Sb, Sc, Sm, Ta, Tb, Yb, Zn, and Zr) and the radionuclides ((238)U, (232)Th, (226)Ra, (228)Ra, (210)Pb and (40)K) in Brazilian clays as well as the health and radiological implications of the use of these clays in pharmaceutical formulations. (C) 2011 Elsevier B.V. All rights reserved.

Polyaniline/layered zirconium phosphate nanocomposites: Secondary-like doped polyaniline obtained by the layer-by-layer technique

In the present work, nanocomposites of polyaniline (PANI) and layered alpha-Zr(HPO4)(2).H2O (alpha-ZrP) were prepared using two different approaches: (i) the in situ aniline polymerization in the presence of the layered inorganic material and (ii) the layer-by-layer (LBL) assembly using an aqueous solution of the polycation emeraldine salt (ES-PANI) and a dispersion of exfoliated negative slabs of alpha-ZrP. These materials were characterized spectroscopically using mainly resonance Raman scattering at four exciting radiations and electronic absorption in the UV-VIS-NIR region. Structural and textural characterizations were carried out using powder X-ray diffraction (XRD) and scanning electron microscopy (SEM). The polymer obtained by the in situ aniline polymerization is located primarily in the external surface of the inorganic material although aniline monomers were intercalated between alpha-ZrP interlayer regions before oxidative polymerization. Through resonance Raman spectroscopy, it was observed that the formed polymer has semiquinone units (ES-PANI) and also azo bonds (-N = N-), showing that this method results in a polymer with a different structure from the usual ""head-to-tail"" ES-PANI. The LBL assembly of pre-formed ES-PANI and exfoliated alpha-ZrP particles produces homogeneous films with reproducible deposition from layer to layer, up to 20 bilayers. Resonance Raman (lambda(0) = 632.8 nm) spectrum of PANI/ZrP LBL film shows an enhancement in the intensity of the polaronic band at 1333 cm(-1) (nu C-N center dot+) and the decrease of the band intensity at 1485 cm(-1) compared to bulk ES-PANI. Its UV-VIS-NIR spectrum presents an absorption tail in the NIR region assigned to delocalized free charge carrier. These spectroscopic features are characteristic of highly conductive secondary doped PANI suggesting that polymeric chains in PANI/ZrP LBL film have a more extended conformation than in bulk ES-PANI.

Effects of alloying elements on the cytotoxic response of titanium alloys

Titanium alloys, alloys, especially beta-type alloys containing beta-stabilizing elements, constitute a highly versatile category of metallic materials that have been under constant development for application in orthopedics and dentistry. This type of alloy generally presents a high mechanical strength-to-weight ratio, excellent corrosion resistance and low elastic modulus. The purpose of this study is to evaluate the cytotoxicity and adhesion of fibroblast cells on titanium alloy substrates containing Nb, Ta, Zr, Cu, Sn and Mo alloying elements. Cells cultured on polystyrene were used as controls. In vitro results with Vero cells demonstrated that the tested materials, except Cu-based alloy, presented high viability in short-term testing. Adhesion of cells cultured on disks showed no differences between the materials and reference except for the Ti-Cu alloy, which showed reduced adhesion attributed to poor metabolic activity. Titanium alloys with the addition of Nb, Ta, Zr, Sn and Mo elements show a promising potential for biomedical applications. (C) 2011 Elsevier B.V. All rights reserved.

Contribuição ao estudo petrográfico e geoquímico dos carvões da jazida de Chico Lomã Santo Antônio da Patrulha

São apresentados os resultados dos estudos petrográfico e geoquímico dos carvões da jazida de Chico Lomã, localizada no município de Santo Antônio da Patrulha, no nordeste do Rio Grande da Sul, situada entre as jazidas de Morungava (limite oeste) e Santa Terezinha (limite leste). Na sondagem estudada - 02-TG-88-RS - foram identificadas 7 camadas e 5 leitos de carvão. Entre estes, apenas as camadas E e F apresentam suficiente extensão lateral para serem consideradas economicamente exploráveis. Os carvões são ricos em matéria mineral, constituída, principalmente, de argila. O grupo maceral mais freqüente é o da vitrinita. No que diz respeito aos microlitotipos, ocorre, em geral, o predomínio de carbominerita. Foram identificadas 3 associações de microlitotipos, determinando a existência das seguintes faciologias: ambiente telmático (predomínio de vitrita-clarita), limo-telmático (predomínio de carbargilita-vitrita) e límnico (predomínio de carbargilita-durita-trimacerita). Os carvões apresentam rank que varia de betuminoso alto volátil C/sub-betuminoso A a betuminoso alto volátil A (ASTM). A utilização tecnológica dos carvões das camadas E e F, na siderurgia, pode ser sugerida, mesmo considerando-se seu elevado teor em cinza, desde que sejam submetidos a processos de beneficiamento. Em relação aos argilo-minerais, constatou-se a presença de caolinita, aparentemente relacionada ao conteúdo da matéria orgânica, e do interestratificado ilita-montmorilonita, provavelmente de origem detrítica. Foram identificados 3 grupos de elementos traços : associados à fração orgânica (Co, Ge, Ni, V e Zr), elementos intermediários (Cr, Cu e Sr) e associados à fração inorgânica (B, Ba e Ga). Observou-se, também, que os elementos do primeiro grupo, de maneira geral, se enriquecem nos litotipos com maior conteúdo de vitrênio, ao contrário dos elementos do último grupo que tendem a se enriquecer no carvão fosco e nos folhelhos. Os estudos realizados indicam um paleoambiente de água doce, no qual, provavelmente, tenham ocorrido pequenas ingressões marinhas entre as fases de formação de turfa.

Filmes finos dielétricos para a tecnologia do silício : processamento térmico e caracterização

O rápido avanço tecnológico coloca a tecnologia do Si diante de um grande desafio: substituir o dielétrico de porta utilizado por mais de 40 anos em dispositivos MOSFET (transistor de efeito de campo metal-óxido-semicondutor), o óxido de silício (SiO2), por um material alternativo com maior constante dielétrica. Nesse contexto, vários materiais têm sido investigados. Nesta tese concentramos nossa atenção em três candidatos: o óxido de alumínio (Al2O3), o silicato de zircônio (ZrSixOy) e o aluminato de zircônio (ZrAlxOy). Nossos resultados experimentais baseiam-se em técnicas de análise com feixes de íons ou raios-X e de microscopia de força atômica. No caso do Al2O3, investigamos a difusão e reação de oxigênio através de filmes relativamente espessos (35 nm) quando submetidos a tratamento térmico em atmosfera oxidante, e os efeitos que esses processos provocam em filmes finos (6,5 nm) de Al2O3 depositados sobre uma estrutura SiO2/Si. Observamos que o processo de difusão-reação em filmes de Al2O3 é diferente do observado em filmes de SiO2: no primeiro caso, oxigênio difunde e incorpora-se em todo o volume do filme, enquanto que em filmes de SiO2, oxigênio difunde através do filme, sem incorporar-se em seu volume, em direção à interface SiO2/Si, onde reage. Além disso, quando oxigênio atinge a interface Al2O3/Si e reage com o Si, além da formação de SiO2, parte do Si migra em direção ao Al2O3, deslocando parte dos átomos de Al e de O. Modelos baseados em difusão e reação foram capazes de descrever qualitativamente os resultados experimentais em ambos os casos. A deposição de filmes de Al2O3 sobre Si por deposição química de camada atômica a partir de vapor também foi investigada, e uma nova rotina de deposição baseada em préexposição dos substratos de Si ao precursor de Al foi proposta. As estruturas ZrSixOy/Si e ZrAlxOy/Si (ligas pseudobinárias (ZrO2)z(SiO2)1-z e (ZrO2)z(Al2O3)1-z depositadas sobre Si) foram submetidas a tratamentos térmicos em oxigênio ou vácuo com o objetivo de investigar possíveis instabilidades. Os tratamentos térmicos não provocaram instabilidades na distribuição de Zr, mas migração e incorporação de Si no filme dielétrico foram observadas durante os dois tratamentos para ambos os materiais.

Síntese de co- e terpolimeros de etileno-propileno através de catalisadores metalocênicos homogêneos e heterogêneos

Neste trabalho, estudaram-se reações de co- e terpolimerização com sistemas metalocênicos, cocatalisadas por metilaluminoxano (MAO). A estrutura destes complexos foi analisada com respeito aos efeitos estéricos e eletrônicos. A otimização da geometria destes complexos foi realizada através de cálculos de campo de força, e os aspectos eletrônicos dos complexos neutros foram analisados por espectroscopia de UV-visível e fotoeletrônica de raios-X (XPS). A performance catalítica destes complexos foi avaliada com relação à atividade, incorporação de propileno, massa molar média e sua distribuição em diferentes condições de polimerização. O sistema catalítico Et(4-Ph-7MeInd)2ZrCl2/MAO foi testado pela primeira vez na literatura aberta para a reação de copolimerização de etileno-propileno obtendo-se altas atividades, alta incorporação de propileno e microestrutura tipo bloco nos copolímeros. A heterogeneização dos sistemas metalocênicos foi avaliada através de três rotas básicas: imobilização diretamente sobre sílica, sobre sílica modificada com MAO e sobre sílica modificada com compostos atuando como espaçadores horizontais. Estes três métodos foram comparados com relação às características finais dos copolímeros. Na etapa de modificação da sílica com MAO, inicialmente estudaram-se as condições de preparação do sistema catalítico, concentração de Zr e Al e temperatura, que poderiam levar a mudanças no produto final. Através de técnicas de análise de superfície como XPS, DRIFTS (Espectroscopia de Infravermelho por refletância difusa) e UV-DRS (Espectroscopia de UV-Visível por refletância difusa) foi possível o estudo das espécies formadas na superfície da sílica modificada com MAO. Os sistemas catalíticos suportados na sílica modificada com espaçadores horizontais mostraram ser mais ativos que o sistema suportado diretamente sobre sílica incorporando distintos teores de propileno. As modificações na superfície da sílica com relação ao teor final de grupos hidroxilas e energia de ligação dos elétrons 3d5/2 do átomo de Zr também foram analisadas. Foi feito o estudo cinético da co- e terpolimerização de etileno-propileno para alguns sistemas metalocênicos estudados. No caso da terpolimerização foi realizado o estudo teórico e experimental da reação de terpolimerização para a síntese de EPDM com o sistema catalítico Et(Ind)2ZrCl2/MAO e 2-etilideno-5-norbornadieno (ENB) como termonômero. Finalmente, este modelo foi adaptado às reações de copolimerização realizadas na primeira etapa do trabalho. As razões de reatividade foram determinadas para os precursores catalíticos Me2Si(2-MeInd)2ZrCl2, Et(IndH4)2ZrCl2, Me2Si(IndH4)2ZrCl2 and Et(4-Ph-7-MeInd)2ZrCl2 e também para os respectivos sistemas suportados em sílica modificada por MAO. Também realizou-se a determinação do coeficiente de transferência de massa convectivo para o etileno e o propileno nas reais condições de polimerização. As razões de reatividade e os parâmetros de transferência de massa foram usados no modelo da reação de copolimerização para sistemas metalocênicos homogêneos e suportado. Este modelo permitiu o discernimento das reações que controlam as características finais dos copolímeros sintetizados.